4430 Antiarrhythmics Practice Exam

Adenosine exerts AV nodal effects through which mechanism?

Blocks Na channels to slow conduction.

Prolongs QT by blocking K channels.

Stimulates calcium influx to accelerate conduction.

Activates A1 receptor in AV node; Reduces cAMP; Opens K channels; Decreases L-type Ca current; Briefly slows or blocks AV conduction.

Adenosine slows AV nodal conduction by activating A1 receptors in the AV node, which engages Gi proteins to reduce cAMP. Lower cAMP decreases L-type calcium current, and this is paired with opening of potassium channels, hyperpolarizing nodal cells. The net effect is to transiently slow or briefly block AV conduction, since AV node activity relies heavily on calcium-driven depolarization and is sensitive to hyperpolarization. This rapid, short-lived action helps terminate reentrant SVTs that pass through the AV node. The mechanism isn’t about blocking sodium channels or prolonging the QT interval; it’s specific to the A1 receptor–Gi–cAMP–K+ channel pathway that reduces calcium influx and increases outward K+ current, tempering AV nodal conduction.